As a shield conductor using a non-shielded wire, there has been one collectively shielding a plurality of non-shielded wires by enwrapping with a shielding member composed of a tubular braided wire made of metal thin wires woven into meshes. As a protecting method for shielding members and wires in this kind of shield conductor, means for enwrapping shielding members with a protector made from synthetic resin has been generally known. However, using a protector causes an increased number of parts.
Considering the foregoing, the applicant of the present application has suggested, as described in Patent Literature 1, a structure wherein a non-shielded wire is inserted into a metal pipe. According to this configuration, the pipe fulfills functions of shielding and protecting wires, and it is therefore advantageous that the configuration requires fewer number of parts, compared to a shield conductor using a shielding member and a protector.
[Patent literature 1]: Japanese Unexamined Patent Publication No. 2004-171952
In a shield conductor using a pipe, an air layer exists between wires and the pipe, and it is therefore difficult for heat generated in wires at the time of energizing to be transmitted to the pipe since the heat is cut off by air of low heat conductivity. Moreover, since no venting pathway to the outside, like the clearance between knitted stitches in braided wires, exists in the pipe, heat generated in the wires is easily confined inside of the pipe. Therefore, a shield conductor using a pipe tends to have a lower radiation performance.
Here, the heating value at the time of applying a prescribed electrical current to a conductor is lower when a cross-section area of the conductor is larger, while a temperature rise value of the conductor caused by heat generation is more restrained when the radiation performance of the electrically-conducting path is higher. Consequently, in an environment where the upper limit of the temperature rise value of the conductor is decided, and in a shield conductor of low radiation efficiency as mentioned above, it is necessary to restrain a heating value by enlarging the cross-section area of the conductor.
However, enlarging the cross-section area of a conductor means an increased diameter and weight of the shield conductor, and therefore requiring a countermeasure.
Thus, there is a need in the art for an improve radiation performance of a shield conductor.